This invention relates generally to aerial lifts and, more particularly, to bucket leveling systems for automatically leveling a bucket of an aerial lift as the bucket is raised and lowered.
Aerial lifts of the type having a passenger bucket or platform mounted at the end of a tower assembly comprised of articulated upper and lower booms, typically require some provision for keeping the bucket level as the angle of the upper boom changes relative to horizontal. In prior art aerial lifts, the bucket is mounted at the end of the upper boom for rotation around a generally horizontal axis, and the rotational position of the bucket is controlled by means of cables housed in the upper and lower booms and reeved over a sheave fixed to the bucket. During use, the cables cause movement of the bucket in response to changes in the angular position of the booms. In addition to providing an automatically leveled bucket, this arrangement locks the bucket against free-swinging rotation around the axis and thus provides, at all times, a rigid working platform regardless of changes in the elevation of the boom assembly. However, the cables in such a lift may be subject to stretching over time and may tend to slap against the interior of the upper and lower booms as the aerial lift is moved from one site to another. Excessive backlash, wear, platform sag, a general loss of effectiveness and a need for frequent readjustment can result.
In view of the foregoing, it is a general object of the present invention to provide an improved bucket leveling system for use in aerial lifts.
It is a more specific object of the present invention to provide an aerial lift bucket leveling system wherein the disadvantages associated with the use of long cables are avoided.